Medical electrodes are used in conjunction with a variety of electronic implantable medical devices such as pacemakers, cardiovertor defibrillators, neurostimulators, and ECG monitors. Medical leads may carry one or more electrodes used for sensing electrical signals in the body, such as intracardiac electrogram (EGM) signals, electrocardiogram (ECG) signals, and electromyogram (EGM) signals. Electrodes are also used for delivering therapeutic electrical stimulation pulses or for delivering electrical pulses used in electrophysiological mapping or for other diagnostic purposes. Leadless electrodes may be incorporated on the housing of an implantable medical device and used for sensing and/or stimulating in combination with other leadless or lead-based electrodes.
In selecting materials for fabricating a medical electrode, considerations include the biocompatibility, electrical properties, mechanical properties, chemical stability, the radiographic visibility of the material and the electrode-tissue interfacial impedance. Known or proposed medical electrodes are fabricated with a base material formed from platinum, titanium, tantalum, stainless steel, iridium, or alloys thereof. Platinum and platinum-iridium provide good electrical and mechanical properties, are chronically biostable and are highly visible under radiography. For these reasons, platinum and platinum-iridium, though relatively costly materials, are commonly used for manufacturing medical electrodes intended for chronic implantation. The electrode base material is often coated with a porous or high surface area coating, referred to as a low polarization coating, to reduce the effects of polarization at the tissue-electrode interface, which can interfere with electrode performance. Known or proposed medical electrode coatings include platinum black, carbon black, platinum oxide, iridium oxide, and porous carbide, nitride, or carbonitride layers formed form titanium, vanadium, zirconium, niobium, molybdenum, hafnium, tantalum, iridium, platinum, and tungsten.